Continuously Flow Photothermal Catalysis Efficiently CO2 Reduction Over S-Scheme 2D/0D Bi5O7I-OVs/Cd0.5Zn0.5S Heterojunction with Strong Interfacial Electric Field

Using CO₂, water, and sunlight to produce solar fuel is a very attractive process, which can synchronously reduce carbon and convert solar energy into hydrocarbons. However, photocatalytic CO₂ reduction is often limited by the low selectivity of reduction products and poor photocatalytic activity. In this study, S-scheme Bi₅O₇I-OVs/Cd_0.5Zn_0.5S (Bi₅O₇I-OVs/CZS-0.5) heterojunction with strong interfacial electric field (IEF) is prepared by in situ growth method. The performance of reduction CO₂ to CO is studied by continuous flow photothermal catalytic (PTC) CO₂ reduction platform. 12.5% Bi₅O₇I-OVs/CZS-0.5 shows excellent CO yield of 58.6 µmol g⁻¹ h⁻¹ and selectivity of 98.4%, which are 35.1 times than that of CZS-0.5 under visible light. The charge transfer path of the S-scheme through theoretical calculation (DFT), in situ irradiation Kelvin probe force microscope (ISI-KPFM) and in situ irradiation X-ray photoelectron spectroscopy (ISI-XPS) analysis, is verified. The study can provide useful guidance and reference for improving activity by oxygen vacancy induced strong IEF and the development of a continuous flow PTC CO₂ reduction system.     

Layer Dependence and Light Tuning Surface Potential of 2D MoS2 on Various Substrates

Here surface potential of chemical vapor deposition (CVD) grown 2D MoS₂ with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS₂ are investigated. The surface potential of MoS₂ on Si/SiO₂ substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS₂ are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO₂, Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS₂, with the increase in light intensity, the surface potential of MoS₂ on Si/SiO₂ substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I–V curves on vertical of monolayer MoS₂/Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS₂/Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field.     

Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

Photocatalytic degradation of 2,4-dichlorophenol wastewater using porphyrin/TiO2 complexes activated by visible light

The use of TiO₂ as photocatalyst to degrade the organic compounds is an effective method of oxidation process and has been widely studied in environmental engineering. However, TiO₂ absorbed the UV light which is only small part of sunlight reaching earth surface to activate photocatalytic procedure effectively is a major disadvantage. Therefore, studies on the development of new TiO₂ wherein its photocatalytic activity can be activated by visible light which is the major part of sunlight will be valuable for field application. In this study, we evaluate the photocatalytic degrading efficiency of porphyrins/TiO₂ complexes on the organic pollutants under irradiation with visible light (λ = 419 nm). The results showed that the photodecomposition efficiency of 2,4-dichlorophenol (2,4-DCP) wastewater by using porphyrin/TiO₂ irradiated under visible light for 4 h was up to 42-81% at pH 10. These evidences reveal that the system of porphyrin/TiO₂ complexes has also significantly efficiency of photocatalytic degradation for some hazardous or recalcitrant pollutants under visible light irradiation.     

Ag2S quantum dots-sensitized TiO2 nanotube array photoelectrodes

Ag₂S quantum dots (QDs) were deposited on ordered TiO₂ nanotube arrays (TNTAs) using a sequential chemical bath deposition (S-CBD) approach. AgNO₃ and thiourea were used as the precursor materials of Ag⁺ and S²⁻ ions, respectively. The decoration of Ag₂S QDs significantly shifted the absorption spectrum of the TNTAs to visible light region. As a result, Ag₂S QDs-sensitized TNTAs exhibited much higher photocurrent density than pure TNTAs under visible light irradiation.     

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution by Plasmonic Au/CdSe–Cu2O Hierarchical Nanostructures under Visible Light

Here, the photocatalytic CO₂ reduction reaction (CO₂RR) with the selectivity of carbon products up to 100% is realized by completely suppressing the H₂ evolution reaction under visible light (λ > 420 nm) irradiation. To target this, plasmonic Au/CdSe dumbbell nanorods enhance light harvesting and produce a plasmon‐enhanced charge‐rich environment; peripheral Cu₂O provides rich active sites for CO₂ reduction and suppresses the hydrogen generation to improve the selectivity of carbon products. The middle CdSe serves as a bridge to transfer the photocharges. Based on synthesizing these Au/CdSe–Cu₂O hierarchical nanostructures (HNSs), efficient photoinduced electron/hole (e^?/h⁺) separation and 100% of CO selectivity can be realized. Also, the 2e^?/2H⁺ products of CO can be further enhanced and hydrogenated to effectively complete 8e^?/8H⁺ reduction of CO₂ to methane (CH₄), where a sufficient CO concentration and the proton provided by H₂O reduction are indispensable. Under the optimum condition, the Au/CdSe–Cu₂O HNSs display high photocatalytic activity and stability, where the stable gas generation rates are 254 and 123 µmol g^?1 h^?1 for CO and CH₄ over a 60 h period.     

Improved performance of dye-sensitized solar cells with laser-textured nanoporous TiO2 photoanodes

This study reports the improved performance of dye-sensitized solar cells (DSSCs) with TiO₂ photoanodes textured by a KrF excimer laser. The excimer laser was employed to create texture for the photoanodes after sintering from TiO₂ pastes at 510 °C. The results revealed that the efficiency increased by 24% (from 4.49% to 5.59%) for cells with photoanodes annealed with 11,200 shots of 80 mJ/cm² laser irradiation. The porous TiO₂ photoanodes became less transparent after the laser treatment, indicating an increase in light trapping due to a rougher texture. A notable enhancement of light absorption for wavelengths greater than 550 nm was achieved. The open circuit voltage (V_oc) and fill factor (FF) were also improved. The surface re-melting and solidification process may change the series and shunt resistances and reduce the surface recombination centers, leading to the increases of V_oc and FF.     

Hydrophilic and photocatalytic properties of the SiO2/TiO2 double layers

The hydrophilic and photocatalytic properties of the SiO₂/TiO₂ double layers composed of a 20-nm-thick porous SiO₂ layer on the 200-nm-thick columnar anatase TiO₂ layer were studied. The hydrophilicity of the double layers was strictly determined by the relative coverage of organic contaminants. The intrinsic hydrophilicity of 0° of SiO₂ in terms of the water contact angle was restored by the photocatalytic decomposition of organic contaminants under the UV light irradiation.Electron spin resonance measurements revealed the generation of OH radicals under the UV light irradiation onto the SiO₂/TiO₂ double layers. Photoconductivity measurements showed that the current decay in O₂ gas atmosphere was remarkably fast in comparison with that in H₂O vapor. These observations support our view that the generation of OH radicals effective for decomposing organic contaminants on the surface begins with the reaction between O₂ molecules and the photoexcited electrons. We propose together with other experimental facts herein that OH radicals would be generated via O₂⁻ and H₂O₂ in the double layer system.     

Determination of photo-catalytic activity of un-doped and Mn-doped TiO2 anatase powders on acetaldehyde under UV and visible light

Titanium dioxide (TiO₂) photocatalytic powder materials doped with various levels of manganese (Mn) were synthesized to be used as additives to wall painting in combating indoor and outdoor air pollution. The heterogeneous photocatalytic degradation of gaseous acetaldehyde (CH₃CHO) on Mn-TiO₂ surfaces under ultraviolet and visible (UV/Vis) irradiation was investigated, by employing the Photochemical Static Reactor coupled with Fourier-Transformed Infrared spectroscopy (PSR/FTIR) technique. Experiments were performed by exposing acetaldehyde (~ 400 Pa) and synthetic air mixtures (~ 1.01 × 10⁵ Pa total pressure) on un-doped TiO₂ and doped with various levels of Mn (0.1-33% mole percentage) under UV and visible irradiation at room temperature. Photoactivation was initiated using either UV or visible light sources with known emission spectra. Initially, the photo-activity of CH₃CHO under the above light sources, and the physical adsorption of CH₃CHO on Mn-TiO₂ samples in the absence of light were determined prior to the photocatalytic experiments. The photocatalytic loss of CH₃CHO on un-doped TiO₂ and Mn-TiO₂ samples in the absence and presence of UV or visible irradiation was measured over a long time period (≈ 60 min), to evaluate their relative photocatalytic activity. The gaseous photocatalytic end products were also determined using absorption FTIR spectroscopy. Carbon dioxide (CO₂) was identified as the main photocatalysis product. It was found that 0.1% Mn-TiO₂ samples resulted in the highest photocatalytic loss of CH₃CHO under visible irradiation. This efficiency was drastically diminished at higher levels of Mn doping (1-33%). The CO₂ yields were the highest for 0.1% Mn-TiO₂ samples under UV irradiation, in agreement with the observed highest CH₃CHO decomposition rates. It was demonstrated that low-level (0.1%) doping of TiO₂ with Mn results in a significant increase of their photocatalytic activity in the visible range, compared to un-doped TiO₂. This elevated activity is lost at high doping levels (1-33%). Finally, the photocatalytic degradation mechanism of CH₃CHO on 0.1% Mn-TiO₂ surfaces under visible irradiation leading to low CO₂ yields is different than that under UV irradiation resulting to high CO₂ yields.     

UV and visible light photodegradation effect on Fe–CNT/TiO2 composite catalysts

Using multi-walled carbon nanotube (CNT) as an one-dimensional support, we have succeeded in uniformly anchoring of TiO₂ and Fe nanoparticles at its surface. The as-prepared Fe–CNT/TiO₂ composite photocatalysts have been investigated by degrading methylene blue (MB) under UV and differently intensified visible light irradiation. The ability of CNT to store and shuttle electrons, and Fe nanoparticles demonstrate its capability to serve as a yield and transfer electrons on demand to separate h^?+?/e^??? pairs. Moreover, the MB photodegradation increase with an increase of visible light intensity can be ascribed to the enhancement MB cationic radical. In addition, chemical oxygen demand (COD) of piggery waste and reduction efficiency of Cr (IV) was done at regular intervals, which gave a good idea about mineralization of wastewater.     

Scalable Synthesis of Holey Deficient 2D Co/NiO Single-Crystal Nanomeshes via Topological Transformation for Efficient Photocatalytic CO2 Reduction

Preparation of holey, single-crystal, 2D nanomaterials containing in-plane nanosized pores is very appealing for the environment and energy-related applications. Herein, an in situ topological transformation is showcased of 2D layered double hydroxides (LDHs) allows scalable synthesis of holey, single-crystal 2D transition metal oxides (TMOs) nanomesh of ultrathin thickness. As-synthesized 2D Co/NiO-2 nanomesh delivers superior photocatalytic CO₂-syngas conversion efficiency (i.e., V_CO of 32460 µmol h⁻¹ g⁻¹ CO and $V_{{\mathrm{H}}_2}$ of 17840 µmol h⁻¹ g⁻¹ H₂), with V_CO about 7.08 and 2.53 times that of NiO and 2D Co/NiO-1 nanomesh containing larger pore size, respectively. As revealed in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the high performance of Co/NiO-2 nanomesh primarily originates from the edge sites of nanopores, which carry more defect structures (e.g., atomic steps or vacancies) than basal plane for CO₂ adsorption, and from its single-crystal structure adept at charge transport. Theoretical calculation shows the topological transformation from 2D hydroxide to holey 2D oxide can be achieved, probably since the trace Co dopant induces a lattice distortion and thus a sharp decrease of the dehydration energy of hydroxide precursor. The findings can advance the design of intriguing holey 2D materials with well-defined geometric and electronic properties.     

Sol-gel synthesis and characterization of the photocatalyst BaCo1/3Nb2/3O3

The photocatalyst BaCo_1/3Nb_2/3O₃ has been synthesized at 750°C by using a sol-gel process, and the surface area is 19.70 m²/g. While the surface area of the powder synthesized by using a solid state reaction process is 2.2 m²/g. It was characterized by X-ray diffraction, scanning electron microscopy(SEM), UV-vis diffuse reflectance spectroscopy, Raman scattering spectroscopy and the measurement of the photocatalytic activity in evolving H₂ from CH₃OH/H₂O solution with the Pt co-catalyst under visible light irradiation. From the SEM image, BaCo_1/3Nb_2/3O₃ powder calcined at 750°C is dispersive, and the average particle size is about 30 nm. Raman scattering spectrum at room temperature shows that, due to the different ionic radius of the Co²⁺ and Nb⁵⁺ ions, BaCo_1/3Nb_2/3O₃ may has a distorted perovskite structure. Under visible light irradiation (λ > 420 nm), the formation rate of H₂ evolution from CH₃OH/H₂O solution with the 0.5 wt% Pt co-catalyst is about 18.1 μmol/h·gcat. for the photocatalyst BaCo_1/3Nb_2/3O₃, much higher than that of BaCo_1/3Nb_2/3O₃ powder synthesized by the solid state reaction process.     

Strongly coupled Ag/TiO<Subscript>2</Subscript> heterojunctions for effective and stable photothermal catalytic reduction of 4-nitrophenol

The development of effective catalysts for the catalytic conversion of the harmful nitrophenol (NP) into the useful aminophenol (AP) has received extensive interest. Herein, we report the easy and large-scale synthesis of strongly coupled Ag/TiO₂ heterojunctions based on the coordinated action of organic components with a multi-kind metal precursor. The heterojunctions were effective and stable catalysts for the photothermal catalytic reduction of 4-NP to 4-AP. In the synthesis, critic acid, ethylene glycol, AgNO₃, and tetrabutyl titanate were dissolved and coordinated in water. Under heating, a precursor gel having a uniform distribution of Ag and Ti was gradually formed. Via calcination in air, the Ti precursor was transformed into TiO₂, accompanied by the reduction of Ag⁺ to Ag nanoparticles. The formation of Ag/TiO₂ composites with intimate interface contact benefited from the uniform distribution of different components in the precursor gel. The Ag/TiO₂ functioned as an effective catalyst for the reduction of 4-NP, exhibiting higher activity than the many reported Ag-based catalysts. The catalytic reaction over Ag/TiO₂ had a small t ₀ with good activity and reuse performance. After 10 cycles of reuse, the conversion efficiency exhibited no obvious change. Importantly, the conversion of 4-NP was significantly enhanced under light irradiation provided by a 150-W Xe lamp (the visible light from cutoff have equal function), but ultraviolet light did not promote the conversion. The conversion time was reduced from 620 to 270 s with light irradiation (15 °C). The reaction rate under light irradiation (0.014 s^?1) was approximately three times higher than that in the dark at 15 °C (0.0044 s^?1) and even better than that in the dark at 25 °C (0.01 s^?1). A series of experiments indicated that the light irradiation promoted the conversion of 4-NP because of the localized surface plasmon resonance effect of Ag, which generated hot e^? and h⁺ particles and local heating around the particles via their absorption of the light.

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Facile preparation and enhanced photocatalytic H2-production activity of Cu(OH)2 nanospheres modified porous g-C3N4

A facile precipitation approach for the preparation of Cu(OH)₂/g-C₃N₄ composite photocatalysts with good porous structure was developed for the first time. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible light (UV–vis) absorbance spectra, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). A photocatalytic water splitting reaction on the as-prepared photocatalysts were carried out under visible light irradiation. The results revealed that the prepared samples showed significantly enhanced photocatalytic activity. The optimal Cu(OH)₂ loading content was found to be 0.34 mol%, giving an H₂-production rate of 48.7 μmol h⁻¹ g⁻¹, which is higher 16.5 times than that of pure g-C₃N₄. This high photocatalytic H₂-production activity is attributed to the presence of Cu(OH)₂ clusters on the surface of the porous g-C₃N₄, which efficiently promotes the visible light absorption and separation of photogenerated electron–hole pairs.     

Influence of metal plasma ion implantation on photo-sensitivity of anatase TiO2 thin films

Nano-scale TiO₂ thin films were synthesized by using sol-gel and spin-coating techniques on glass substrates for photo-catalytic applications. The Ti(IV) butoxide-based TiO₂ thin films were optimized for transforming into the high-purity crystalline anatase phase when calcined at 500 °C. To further enhance the photo-catalysis sensitivity of TiO₂ thin films for use in visible light environments, a metal plasma ion implantation process was implemented to modify the band gap electron configuration of Ti. Various transition metal atoms such as Ni, Cu, V, and Fe were ionized and accelerated at 20 keV to impinge on the surface of TiO₂ substrates at a dosage of 5 × 10¹⁵ ions/cm². ESCA analysis confirmed the binding energy shift of Ti by 0.8-1.2 eV, which accounted for the increased effective positive charge of Ti, resulting in more effective electron trapping capability and, thus, the electron-hole pair separation. In addition, the absorption spectroscopy demonstrated that optical absorption in the visible light regime occurred in specimens implanted with transition metal ions, likely due to the formation of extra impurity energy levels within the original TiO₂ band gap energy structure. Among all tested implant materials, the band gap energy of TiO₂ was effectively reduced by Cu and Fe ion implantation by 0.9-1.0 eV, which was sufficient enough to excite valence electrons over the band gap in visible light environments. The feasibility of the metal-doped TiO₂ thin films for effective applications under visible light irradiation was further confirmed by using super-hydrophilicity contact-angle measurement.     

UV-TiO2 photocatalysis-assisted chemical mechanical polishing 4H-SiC wafer

The objective of this study is to propose a photocatalysis-assisted chemical mechanical polishing (PCMP) method for atomic smoothing SiC wafer based on the powerful oxidability of UV photo-excited hydroxyl radical on nano-TiO₂ particles. The study identifies five slurries of different photocatalyst, electron capturer, UV light, and pH value by measuring oxidation reduction potential and static oxidation experiment. After PCMP process, a SiC wafer is examined with optical microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy for information on surface finish and quality, material removal and mechanisms. The study demonstrates that photocatalyst, UV light, electron capturer, and acid environment are necessaries for PCMP process. Among the five PCMP slurries, the one with 1?g of TiO₂, 0.3?g of (NaPO₃)₆, 10?ml H₂O₂, 5?g SiO₂ abrasives under UV light irradiation provides the highest material removal rate of 0.95?µm/h and the best surface finish (Ra?=?0.35?nm) and surface quality. It then discusses how UV light irradiation promotes the chemical oxidation of hydroxyl radical with SiC by forming “Si–C–O,” “Si–O,” “C–O,” and “C?O” on SiC surface. The study concludes that the proposed PCMP is effective and clean manufacturing method for SiC wafer without releasing toxic chemicals to environment and human health.     

聚乙二醇辅助光化学制备SnO2及其光催化性能

采用硫酸亚锡作为锡源,加入4种不同分子量的聚乙二醇(PEG),于低功率紫外光辐照下制备二氧化锡。通过X射线衍射(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)和比表面测试对其结构与形貌进行表征。考察聚乙二醇分子量变化对产物结构和光催化性能的影响。所制备SnO2的形貌尺寸、比表面积以及其光催化性能与使用PEG的分子量密切相关,分子量越大,所制备SnO2粉体尺寸越小,分布越均匀。以甲基橙为目标降解物进行光催化实验,结果表明,分子量为6000的聚乙二醇诱导制备的二氧化锡在模拟可见光和紫外光照下均显示了较高的催化活性。     

Photocatalytic effects for the TiO2-coated phosphor materials

This study investigated the photocatalytic behavior of the coupling of TiO₂ with phosphorescent materials. A TiO₂ thin film was deposited on CaAl₂O₄:Eu²⁺,Nd³⁺ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aqueous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO₂-phosphorescent materials, two different samples of TiO₂-coated phosphor and TiO₂–Al₂O₃-coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO₂-coated phosphor powders were different from those of the pure TiO₂ and TiO₂–Al₂O₃-coated phosphor. The absorbance in a solution of the ALD TiO₂-coated phosphor decreased much faster than that of pure TiO₂ under visible irradiation. In addition, the ALD TiO₂-coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO₂–Al₂O₃-coated phosphor did. The TiO₂-coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS).     

A new coral structure TiO2/Ti film electrode applied to photoelectrocatalytic degradation of Reactive Brilliant Red

A novel structure TiO₂/Ti film was prepared on a titanium matrix using anodic oxidation technique and applied to degrade Reactive Brilliant Red (RBR) dye in simulative textile effluents. The film was characterized by Field-Emission Scanning Electron Microscope (FE-SEM), Laser Micro-Raman Spectrometer (LMRS), UV–vis spectrophotometer (UVS) and Photoelectrocatalytic (PEC) experiment. The results show that the surface morphology of the film is coral structure, and the crystal structure of the film is anatase. The absorbency of the coral structure TiO₂/Ti film is 87–93% in the UV light region, and 77–87% in the visible light region. PEC experiment indicates that the photocurrent density of the coral structure TiO₂/Ti film electrode achieves 160 μA/cm². The color and Chemical Oxygen Demand (COD) removal efficiencies of RBR achieve 73% and 60% in 1 h, respectively. These are 16% and 58% higher than those of nanotube TiO₂/Ti film electrode. These were attributed to that these electrodes with different surface morphologies exhibit distinct surface areas and light absorption rate.